JPH0571548B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an inorganic porous structure such as a filtration membrane or a porous support to which a filtration layer is attached and supports it. (Prior art) In this type of inorganic porous structure, if it is a filtration membrane, it must have high filtration accuracy, and if it is a porous support, it must have good adhesion to the filtration layer. It is necessary that the filtration layer has good properties and that no pinholes or cracks are generated in the layer when attaching it, but it must also have high strength and high corrosion resistance, especially excellent alkali resistance, and elution of components is extremely small. It is also necessary. However, Japanese Patent Application Laid-Open No. 61-500221 discloses an inorganic porous structure that is said to have high filtration accuracy and high strength. Such a porous structure consists of at least 99.9wt% α-Al ₂ O ₃ and 29μ
It is manufactured by firing a molded product whose main raw materials are 40 wt% alumina of m. (Problem to be Solved by the Invention) By the way, such a porous structure is composed of a group of particles in substantially the same range due to high temperature firing in a reducing atmosphere, and there are few contact points between particles and the strength is not sufficient. Therefore, a high firing temperature of 1800°C is required, and since the particles are not closely packed, coarse pores are likely to form, resulting in insufficient filtration accuracy, and when used as a support, the attached filtration layer This will cause pinholes and cracks. In addition, since such a porous structure is composed of at least 99.9wt% α-Al ₂ O ₃ , it exhibits relatively good corrosion resistance, but on the high alkali side, Al ₂ O ₃
Intergranular corrosion occurs, causing elution of Al components and detachment of Al ₂ O ₃ particles, resulting in reduced strength and durability. On the other hand, in the manufacturing method as well, the operation control of the firing furnace is complicated due to high temperature firing in a reducing atmosphere, which increases both the equipment cost and the operating cost. Furthermore, the shrinkage of the porous structure during firing reaches 10% or more, and the occurrence of pinholes, cracks, etc. due to the shrinkage is unavoidable. Therefore, an object of the present invention is to solve the above-mentioned problems in an inorganic porous structure mainly composed of α-Al ₂ O ₃ and a method for producing the same. (Means for Solving the Problems) The present invention provides an inorganic porous structure in which fine particles of α-Al ₂ O ₃ adhere to each other to form a porous structure, and the porous structure are (1) to (3) below.
It is characterized by the matters described in section. (1) It consists of at least two particle groups, and the ratio of the largest average particle size to the smallest particle size (particle size ratio) among the average particle sizes of all these particle groups is in the range of 1.4 to 10. (2) In the inorganic porous structure according to item 1,
The fine particles consist of two particle groups. (3) In the inorganic porous structure according to item 1 or 2, the particle size ratio is 1.4 to 4. Further, the present invention is a method for manufacturing such a porous structure, and the manufacturing method is characterized by the matters described in the following items (4) to (9). (4) Consisting of at least two particle groups, the average particle diameter of all these particle groups is 2.0 μm or more, and the largest average particle size and the smallest average particle size among the average particle sizes of all these particle groups Diameter ratio (particle size ratio)
is in the range of 1.4 to 10, an aluminum compound with an average particle size of 1.0 _μm or _less is added to 1 to 15 wt% in terms of oxide, and a titanium compound is added in 0.1 to 0.5 wt% in terms of oxide. The resulting molded product is molded using the main raw materials of
Fire at a temperature below 1600℃. (5) In the manufacturing method described in paragraph 4, the average particle diameter
α-Al ₂ O ₃ of 2.0 μm or more consists of two particle groups. (6) In the manufacturing method according to item 4 or 5, the particle size ratio is 1.4 to 4. (7) In the production method according to item 4, 5, or 6, the aluminum compound is a mixture of alumina and aluminum hydroxide. (8) In the manufacturing method according to item 4, 5, 6, or 7, the firing temperature is 1400 to 1600°C. (9) Section 4, 5, 6, 7 or 8
2. The method for producing an inorganic porous structure, wherein the titanium compound is titanium oxide with an average particle size of 1.0 μm or less. Therefore, in the present invention, the particle diameter of the fine particles constituting the porous structure is measured using an electron microscope (scanning electron microscope), and the statistical average diameter is taken as the particle diameter. Statistical average diameters include Feley's diameter, maximum diameter in a given direction, projection circle equivalent diameter, Martin diameter, etc.
Any of these may be adopted. The number of times the particle diameter is measured is any number that can be statistically processed, usually 100 or more. Further, the particle size of the fine particles of the raw material may be measured using an electron microscope in the same manner as described above, or a sieving method or a sedimentation method may be adopted as a simple method. In addition, the fine particles that make up the porous structure exist in a fixed state, and if the grain boundaries are clear, they are determined to be a single particle with grain boundaries, and the particles are fused together to form a single particle. If the boundary is not clear, the fused material is determined to be a single particle. From the particle diameters of a large number of particles obtained by this measurement method, an integrated sieve particle size distribution curve and a number frequency distribution curve are drawn to determine the number of particle groups and the average particle diameter. When there is a single particle group, the number frequency distribution curve has a shape close to a normal distribution, and the integrated sieve particle size distribution curve can be expressed as a substantially straight line on normal probability paper according to the law of lognormal distribution. On the other hand, when there are a plurality of particle groups, the number frequency distribution curve has a plurality of peaks, and the integrated sieve particle size distribution curve no longer follows the law of lognormal distribution and deviates significantly from the above-mentioned straight line.
The number of particle groups and the average particle diameter can be calculated by mathematical methods, but the number of peaks in the number frequency distribution curve can be used as the number of particle groups, and the above peak can be used as the average particle size. be able to. By the above method, when there are three or more particle groups, the maximum average particle size and the minimum average particle size among the average particle sizes of all these groups are determined, and the ratio of these (particle size ratio) is calculated. Seek. In addition, when there are two particle groups, the average particle diameter of the large-diameter particle group becomes the maximum average particle diameter, and the average particle diameter of the small-diameter particle group becomes the minimum average particle diameter. (Operations and Effects of the Invention) In the porous structure of the present invention, the particles are firmly fixed to each other by the sintering promoting effect of the titanium compound, and grain growth is caused, and at least two types of large and small particles are formed. The particles of the particle group are in a close-packed state, increasing the number of contact points, and are fixed at these contact points. For this reason, such a porous structure has high strength and has no large pores, so it has high filtration accuracy when used as a filtration membrane, and when used as a support for a filtration layer, pinholes, cracks, etc. occur in the same layer. I have nothing to do. Furthermore, due to the presence of titanium compounds, such porous structures have extremely excellent corrosion resistance. In addition, in the porous structure of the present invention, when focusing on the diffusion resistance of the permeating fluid, it is preferable that it consists of two types of particle groups, large and small, and when it consists of three or more types of particle groups, the diffusion resistance of the fluid is large. Become. The amount of titanium compounds mixed is 0.1~
0.5wt% is preferable; if it is less than 0.1wt%, strength will not be sufficiently developed and corrosion resistance will be poor, and
If it exceeds 0.5wt%, the sintering promotion effect is too large and the stress generated during firing causes a decrease in strength. In addition, the purity of α-Al ₂ O ₃ in the porous structure is
It is preferably 99.5wt% or more. The ratio of the largest average particle diameter to the smallest average particle diameter among the average particle diameters of all particle groups (particle size ratio), or if it consists of both large and small particle groups, the particle size ratio of the average particle sizes of both particle groups A value in the range of 1.4 to 10 is preferable; if it is less than 1.4, the difference in particle size is small and there are few contact points (fixing points) between particles, and the strength is not sufficient and the formation of coarse pores is observed. If the difference in particle size is too large, the pore size becomes small and the particles of the particle group with the smallest average particle size increase the diffusion resistance of the fluid. In order to obtain a porous structure with particularly high strength and high porosity, the particle size ratio is preferably 1.4 to 4. In this case, the ratio between the average pore diameter and the maximum pore diameter of the porous structure is, for example, within 2.0,
This results in an extremely sharp pore distribution. In addition, the porosity is 35 to 45%, indicating high porosity. In the method for producing a porous structure of the present invention, α
-Using Al ₂ O ₃ with ultrafine particles of alumina, aluminum compounds such as aluminum hydroxide, and titanium compounds added as the main raw material,
During sintering, the aluminum compound acts to promote sintering and firmly bonds the α-Al ₂ O ₃ particles to each other, while the titanium compound further acts to promote sintering to further firmly bond the particles to each other, and prevents intergranular corrosion. Provides excellent corrosion resistance. Due to the firing accelerating effect of both these compounds, firing is performed in an oxidizing atmosphere at 1600℃.
The temperature may be lower than ℃, preferably 1400~1600℃,
When the firing temperature exceeds 1,600°C, the sintering state progresses too much, impairing porosity and causing cracks due to shrinkage. In the production method of the present invention, the aluminum compound is ultrafine alumina containing aluminum hydroxide with an average particle diameter of 0.1 to 1.0 μm, and it is preferable to add 1 to 15 wt% of these to the main raw material. If the particle size of such a compound exceeds 1.0 μm, the effect of promoting sintering is low, and the same is true even if the amount added is less than 1 wt%, and if the amount added exceeds 15 wt%, the effect of promoting sintering is too large, causing porosity. increases the diffusion resistance of the depleting fluid. Fine-grained alumina hydroxide may be added in the form of a powder or in the form of a sol-like liquid. Examples of the titanium compound include titanium oxide, metal salts, and hydroxides obtained by hydrolyzing metal salts, and ultrafine particles with an average particle size of 1.0 μm or less are preferable. Further, the amount of such a compound added is preferably 0.1 to 0.5 wt% from the viewpoint of sintering promotion effect and corrosion resistance improvement effect. (Example) (1) Main raw material Commercially available fused alumina of various average particle sizes (purity
99.9% α-Al ₂ O ₃ ) to which ultrafine aluminum compound and titanium compound were added was used. However, as aluminum compounds, commercially available high purity α-
Al ₂ O ₃ (purity 99.9%), commercially available alumina sol (A ₁ …
Alumina sol 520) manufactured by Nissan Chemical Co., Ltd., average particle size
0.6 μm commercially available fine aluminum hydroxide (A ₂ )
The titanium compound used was commercially available TiO ₂ fine powder (rutile type) with an average particle size of 0.04 μm.
T ₁ ), reagent titanyl sulfate (added as an aqueous solution...T ₂ ),
Commercially available TiO ₂ powder (rutile type...T ₃ ) with an average particle size of 0.3 μm was used. (2) Preparation of sample Mix the main raw materials in the proportions shown in Table 1, add water, an organic binder (methyl cellulose), and a surfactant (polyester type), knead, and form into a pipe using an extruder. Extruded. After drying the obtained extruded product, it was heated at 1200 °C in an oxidizing atmosphere.
Baked at ~1600℃ for 3 hours, outer diameter 7 mm, inner diameter 5
A pipe-shaped sintered body with a length of 200 mm and a length of 200 mm was obtained. (3) Measurement of characteristics Maximum pore diameter: Measured by bubble point method (μ
m) Average pore diameter: Measured by mercury porosimetry (μm) Pure water permeability: Filter by adding distillation suction at ΔP=0.1Kg/cm ² and measure water permeation (m ³ /m ²・hr) Internal pressure Strength: A rubber tube is set inside a pipe-shaped sintered body, and water is injected into the rubber tube to increase the pressure and measure the pressure at break (Kg・f/cm ² )...Pressure test Fine particles: Particle size is measured using scanning electron The Feley diameter (μm), the number of particle groups, and the average particle diameter are determined using a cumulative sieve particle size distribution curve and a number frequency distribution curve using a microscope. The above characteristics are shown in Table 2 and Figures 1 to 3, and the sintered body of Test No. 13 is shown in Table 3 as a representative example of the cumulative particle size on the sieve, the number frequency, and their distribution curves. and shown in FIGS. 4 and 5. Further, FIG. 6 shows a scanning electron microscope photograph of the same sintered body. In addition, in the integrated sieve particle size distribution curve shown in FIG. 4, the one in test No. 13 (solid line graph) shows a clearly different curve compared to the one in a single particle group (dotted chain line graph), Further, in the number frequency distribution curve, Test No. 13 shows two peaks. In this example, these two peaks are determined as two large and small particle groups, and the particle size of the same peak is determined as the average particle size of each particle group, and the ratio thereof is determined as the particle size ratio. (4) Test results (4a) Particle size ratio As is clear from the results of Tests No. 1 to No. 5 (see Figure 1), the internal pressure strength of the sintered body takes a maximum value with respect to the particle size ratio. , exhibits high strength when the particle size ratio is 1.4 or more. The amount of water permeation decreases as the particle size ratio increases, and since a larger amount of water permeation is practically preferable, the particle size ratio is 10 or less. In view of the relationship between internal pressure strength and water permeability, the most preferable range of particle size ratio is 1.4 to 4. In the results of other test numbers, the particle size ratio
Anything in the range of 1.4 to 10 poses no practical problem;
When composed of three particle groups (test
The same applies to No. 6 and No. 7). however,
If it does not contain titanium compounds (test
In No. 10), both performances were poor even if the particle size ratio was in the range of 1.4 to 10. (4b) TiO ₂ mixed amount As is clear from the results of Test No. 10 to No. 15 (see Figure 2), the internal pressure strength takes a maximum value with respect to the TiO ₂ amount, and at 0.1 to 0.5 wt.%. Shows high strength. In addition, regarding water permeability, TiO ₂
From the above results, the TiO ₂ content increases rapidly to 0.3wt% and then increases slightly.
is preferred. Note that this value corresponds to the amount of the titanium compound added in terms of oxide. (4c) Types of titanium compounds As is clear from the results of Tests No. 13 and No. 22 to No. 25, even if the titanium compound is added as TiO ₂ powder (T ₁ ), the aqueous solution of metal salt (T Even if it is added as ₂ ), there is no change in the properties of the sintered body. However, TiO ₂ (T ₃ ) with large particle size
When TiO 2 is added, the internal pressure strength is reduced because TiO ₂ is not well dispersed in the raw material. (4d) Ultrafine aluminum compound As is clear from the results of Test No. 13, No. 16 to No. 21 (see Figure 3), α-Al ₂ O containing no aluminum hydroxide and having an average particle diameter of 0.6 μm. ₃
When added (circled in the graph), the amount added is 1.
Shows high internal pressure strength and high water permeability at ~15wt%. In addition, when aluminum hydroxide is included (triangle mark on the graph), water permeability decreases;
Internal pressure intensity increases significantly. In addition, the amount added is
If it exceeds 15 wt%, water permeability decreases, which is not preferable. Note that the characteristics do not change depending on the state in which it is added. (4e) Particle size of large particle group As is clear from the results of Tests No. 8, No. 9, and No. 13, the particle size of large particle group is high for those with an average particle size of 10 to 68 μm. Shows internal pressure strength and high water permeability. However, water permeability changes depending on the average pore diameter. (4f) Mixing ratio of large particles
When the blending ratio of small particles is 5wt% or more, high internal pressure strength and high water permeability are exhibited. When the blending ratio of large particles is 45wt%, water permeability is low. (4g) Firing temperature As is clear from the results of Tests No. 13, No. 29, and No. 30, when the firing temperature is 1400 to 1600°C, high internal pressure strength and high water permeability are exhibited. The firing temperature is
At 1200℃, both characteristics are low. (5) Firing comparison test: Same base material as Test No. 10, which does not contain TiO ₂ .
Using the same substrate as Test No. 13 containing 0.3 wt% TiO ₂ , it was fired in a hydrogen atmosphere at 1550°C and 1800°C for 3 hours to obtain a sintered body with the characteristics shown in Table 4. As is clear from Table 4, when the material containing no TiO ₂ is reduced and fired (Test No. 32, No. 33)
It shows high internal pressure strength for the first time when fired at a high temperature of 1800℃. However, in this case, the maximum pore diameter is too large compared to the average pore diameter. When reducing and firing materials containing TiO ₂ (Test No. 34, No.
35) shows a high degree of utilization of internal pressure by firing at 1550°C, but the maximum pore diameter is too large compared to the average pore diameter. Since reduction firing has a stronger sintering effect than oxidation firing, the particles in the small diameter particle group repeat grain growth and the particle ratio increases.
1.4 or less, and in this case, it is difficult to develop strength. In addition, stress due to thermal contraction occurs and cracks are likely to occur, the strength does not increase as much as it appears, and the maximum pore diameter increases.
When a material containing TiO ₂ is reduced and fired at 1800°C, it exhibits high strength but low water permeability. This is because the sintering progressed, the pores became smaller, and the porosity decreased to 30% or less. (6) Corrosion resistance results Using four types of sintered bodies of test No. 10, No. 13, No. 32, and No. 33, PH = 0 (HCl aqueous solution), PH = 14
(NaOH aqueous solution) 1 at 90° C. for 168 hours, and the weight loss rate, amount of Al component eluted, and internal pressure strength after immersion were measured, and the results shown in Table 5 were obtained. As is clear from Table 5, in Test No. 13 (Example), both the weight loss rate against acids and alkalis and the amount of Al component eluted are small, the internal pressure strength remains unchanged, and the corrosion resistance is good. be. The other samples (comparative examples) have problems with corrosion resistance, and the test No. 33 (comparative examples) has a relatively small weight loss rate, but the amount of elution of the Al component and the internal pressure strength are greatly reduced. (7) Film formation test Using two types of sintered bodies, test No. 13 and No. 34, α- with an average particle size of 2.0 μm was coated on the inner periphery of these sintered bodies.
After supporting slurry consisting of Al ₂ O ₃ and drying
Sintered at 1350℃, thickness 50μm, average pore diameter
A thin film of 0.8 μm was formed. When the maximum pore diameter of the obtained thin film was measured using the bubble point method, it was 1.5 μm in Test No. 13 (Example), while that in Test No. 34 (Comparative Example) was 1.5 μm.
It was 6.2 μm. Although the average pore diameter of each sintered body is the same, the reason why the maximum pore diameter of the obtained thin films differs greatly is that the maximum pore diameter of the sintered body of test No. 13 is small, and each pore diameter is relatively uniform. In addition, when we conducted a filtration experiment of a liquid containing latex beads with an average particle size of 3.0 μm using these thin films, test No.
Test No. 13 had a blocking rate of 100%, while test No. 34 had a blocking rate of 85%.

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【table】 [Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the particle ratio of the average particle size of large and small particle groups, internal pressure strength, and water permeability in a sintered body (porous structure), and Figure ₂ is a graph showing the relationship between the particle ratio of the average particle size of large and small particle groups, internal pressure strength, and water permeability in the same sintered body. Figure 3 is a graph showing the relationship between the ultrafine aluminum compound, internal pressure strength, and water permeation in the same sintered body, and Figure 4 is the cumulative amount of the same sintered body. The particle size distribution curve on the sieve, Figure 5 is the number frequency distribution curve of the same sintered body,
FIG. 6 is an electron micrograph showing the internal structure of the sintered body.

Claims (1)

[Claims] 1. An inorganic porous structure in which fine particles of α-Al ₂ O ₃ adhere to each other to form a porous structure, and the structure is composed of at least two particle groups. The ratio of the maximum average particle size to the minimum average particle size (particle size ratio) among the average particle sizes of all these particle groups is in the range of 1.4 to 10, and the titanium compound is 0.1 in terms of oxide. An inorganic porous structure characterized by containing ~0.5wt%. 2 In the inorganic porous structure according to item 1,
An inorganic porous structure consisting of two groups of fine particles. 3. The inorganic porous structure according to item 1 or 2, having a particle size ratio of 1.4 to 4. 4 Consisting of at least two particle groups, the average particle diameter of all these particle groups is 2.0 μm or more, and the maximum and minimum average particle diameters of all these particle groups are The ratio (particle size ratio) is 1.4
α- _Al2O3 in the range of ~10, with _an average particle size of 1.0μ
m or less aluminum compound in terms of oxide
15wt%, titanium compound 0.1~ in terms of oxide
1. A method for producing an inorganic porous structure, which comprises molding a main raw material containing 0.5 wt% and firing the molded product at a temperature of 1600°C or lower in an oxidizing atmosphere. 5 In the manufacturing method described in Section 4, the average particle diameter
A method for producing an inorganic porous structure consisting of two groups of α-Al ₂ O ₃ particles of 2.0 μm or more. 6. A method for producing an inorganic porous structure having a particle size ratio of 1.4 to 4 in the method according to item 4 or 5. 7. The method for producing an inorganic porous structure according to item 4, 5, or 6, wherein the aluminum compound is a mixture of alumina and aluminum hydroxide. 8. The method for producing an inorganic porous structure according to item 4, 5, 6, or 7, wherein the firing temperature is 1400 to 1600°C. 9 Clause 4, Clause 5, Clause 6, Clause 7 or Clause 8
2. The method for producing an inorganic porous structure, wherein the titanium compound is titanium oxide with an average particle size of 1.0 μm or less.